1. Field of the Invention
The present invention relates to methods of forming a pattern on a workpiece by etching the surface of the workpiece, and more particularly to methods especially suitable for forming a pattern on the surface of a strip workpiece.
2. Description of the Prior Art
Manufacture of various articles by etching of the surfaces of workpiece using lithography technique is extensively used in industrial fields, especially in an electronic manufacturing field. According to this process, articles having the same pattern can be mass-produced. In this case, the surface of workpieces are coated with photoresist, the coated photoresist are exposed through a desired pattern and then developed. The surfaces of the workpieces are then etched using the exposed resist as a mask.
However, if the workpieces is a strip workpiece, example a strip image sensor, pattern exposure can not often be effected at a stroke due to restrictions on an exposure device, etc. Thus, in this case, division exposure is performed, i.e. two or more portions into which the pattern surface is divided are exposed one at a time. In order to perform an offsetless pattern formation using a plurality of the division exposure steps, an alignment mark will be formed in advance to the surface of the workpiece.
More particularly, for example, an A 1 film, covering a surface of a workpiece, is coated with photoresist, exposed through an alignment mark pattern and developed. A small portion of the A 1 film containing the mark pattern is etched to remove the photoresist in the small portion and form an alignment mark. The workpiece is then washed and coated with photoresist again. One half of the workpiece extending from the alignment mark in one direction is exposed through one half of a strip pattern and the other half of the workpiece extending from the alignment mark in the opposite direction to the one direction mentioned above is exposed through the other half of the strip pattern. The workpiece is then developed and etched to form a pattern on the workpiece. Finally the photoresist is removed. A flowchart of the steps of this conventional pattern forming process is shown in FIG. 3. However, this process includes relatively many steps, thereby resulting in a low yield.